Animating parts of an object
Two (of many) ways to do it:

Select the radar in edit mode and press P to have it separated in a new object, and animate the whole object, without even the need of an armature.

Or

Create an armature which has a "Radar" bone, parent (Ctrl P) the mesh to the armature and choose "with empty groups" option, then in edit mode select all vertices of the radar, select in the properties panel the newly created "Radar" vertex group and click the "assign" button.